PREPARATION AND PROPERTIES OF RIGID POLYURETHANE FOAMS CONTAINING MODIFIED CORNSTARCHES

Rigid polyurethane foams were prepared containing 20% (based on weight of polyol) unmodified or modified cornstarches. The cornstarches had been modified by breeding or conversion methods and included waxy, acid-modified waxy, malto-dextrin, and canary dextrin. Due to its more favorable role as an extender, canary dextrin was added to additional foam formulations at 10-40%. Foams containing dextrins responded to compressive stress as control foams with yield points before 10% deformation. Foams filled with the unmodified or waxy cornstarches did not give clearly defined yield points and were measured at 10% deformation. After 14 days under 70-degrees-C and ambient conditions, volume increases for the filled foams were 4.0 - 7.1% vs. 4.6% for the control. The foams filled with canary dextrin increased in volume 4.3% With the addition of 40% canary dextrin, the volume increases for the foams were 4.4% under thermal conditions and 4.5% under humid conditions (38-degrees-C and 98% relative humidity). Under humid conditions for 14 days, the foams containing canary dextrin increased in weight as dextrin content increased (1.5, 3.2, 3.4, and 7.6% with 10, 20, 30, and 40% dextrin, respectively). With 40% canary dextrin in the foams, thermal conductivity was 0.0235 vs. 0.0242 W/mK (0.163 vs. 0.168 Btu in/ft2h-degrees-F) for the control.